Grinding machine having a grinding tool for generating grinding of two workpieces

ABSTRACT

Grinding machine having a tool spindle for receiving and rotationally driving a grinding tool about a tool axis of rotation, having a first workpiece spindle for receiving a first workpiece, and having a second workpiece spindle for receiving a second workpiece, wherein the first workpiece spindle and the second workpiece spindle are arranged on one longitudinal side of the grinding tool received on the tool spindle, and both workpiece spindles are arranged parallel to one another.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119(a)-(d) to European application no. EP 14 198 671.1 filed Dec. 17, 2014, which is hereby expressly incorporated by reference as part of the present disclosure.

FIELD OF THE INVENTION

The subject matter of the invention is a device for generating grinding, which comprises two workpiece spindles.

BACKGROUND OF THE INVENTION

There are various concepts for the arrangement of the individual axes in machines, which are designed for machining workpieces. In this case, one attempts, on the one hand, to achieve an optimum cost-usage ratio. On the other hand, above all in mass production, value is frequently laid on the productivity, or the throughput of such a machine.

Machines are known which are based on a tool exchange, to be able to provide the suitable tool in each case for machining a workpiece depending on the machining phase. Such machines can have a tool revolver, for example, which is rotatable. Other machines operate with workpiece axes which are arranged so they are pivotable. For example, a machine according to EP 2305409 B1 comprises two workpiece spindles, which are pivoted about a respective pivot axis for the purpose of movement from a grinding position to a loading position and vice versa. Another type of machine has one grinding tool and at least two workpiece spindles, which are mounted so they are rotatable on a carrier. Depending on the rotational position of the carrier, either a first or a second workpiece can be machined using the grinding tool. Such a machine is known, for example, from EP 1146983 B1.

Another machine has at least one tool spindle having grinding tool and two workpiece spindles, which can be moved individually toward the tool spindle for the interaction of the respective workpiece with the grinding tool. For this purpose, each of the tool spindles is movable in a translational manner along a separate linear guide from a grinding position to a loading position and vice versa. Such a machine can be inferred from document DE 202009013263 U1.

SUMMARY OF THE INVENTION

An object of the present invention is to develop a machine configuration for a grinding machine for machining gearwheels, which, with a simple technical/mechanical structure, has a reproducible high precision of the grinding machining and nonetheless a high throughput.

In particular, it relates to providing a grinding machine for the generating grinding of spur gears, which enables a uniform high precision of the alternating grinding machining of multiple workpieces.

FIG. 1 shows the elements of an exemplary grinding machine 10, wherein in this illustration only the essential elements are identified, specifically these are the tool spindle 1 together with a grinding tool 2, a workpiece spindle 3 having a workpiece W1, and a workpiece spindle 4 having a workpiece W2. In addition, the six axes which are required for the generating grinding of the workpiece W1 or the workpiece W2 are shown in this illustration. Three linear axes X, Y, and Z are used here. In addition, there is an axis of rotation B, to be able to rotationally drive the grinding tool 2 in one direction. The tool spindle 1 together with the grinding tool 2 can be pivoted about a pivot axis A. Furthermore, there is an axis of rotation C1, to be able to rotationally drive the workpiece W1, and an axis of rotation C2, to be able to rotationally drive the workpiece W2. It can be recognized on the basis of FIG. 1 that an entire array of coordinated linear, rotational, and pivot movements are required to be able to perform generating grinding of a workpiece W1 or a workpiece W2 using a grinding tool 2.

Above all in mass production it is important that in machines in which two workpieces are successively machined using the same tool, the quality of the machining of the two workpieces is identical.

In generating grinding, a strong spindle drive is required for rotationally driving the grinding tool 2 about the tool axis of rotation B. The motor which is used as the spindle drive is seated coaxially to the tool axis of rotation B, directly in the region of the grinding tool 2, as shown in FIG. 1. If one wished to arrange this motor differently, for example, an angular gear would have to be provided between the motor and the spindle axis B. The occurring rolling deviations typically result in vibrations, which finally results in inaccuracies on the workpiece.

The structural size of the motor for rotationally driving the grinding tool 2 is accompanied by spatial restrictions, since a collision of the motor with the workpiece has to be avoided in every case. For example, if one wished to arrange the workpiece W2 on the right adjacent to the first workpiece W1 in the machine 10 according to FIG. 1, as shown here solely as an example, the grinding tool 2 together with spindle 1 could hardly still be moved toward the first workpiece W1, without the spindle 1 colliding with the second workpiece W2.

According to certain embodiments of the present invention, a grinding machine is used, which is equipped with a tool spindle for receiving and rotationally driving a grinding tool about a tool axis of rotation and with a first workpiece spindle for receiving a first workpiece and with a second workpiece spindle for receiving a second workpiece. In this grinding machine, the first workpiece spindle and the second workpiece spindle are arranged on one longitudinal side of the grinding tool received on the tool spindle. Both workpiece spindles are arranged parallel to one another (and vertically in relation to a machine bed). The tool spindle is mounted so it is displaceable along a first linear guide, wherein this guide extends in parallel to a horizontal inclined axis. The first workpiece spindle and the second workpiece spindle are spaced apart with the same perpendicular horizontal distance from this horizontal inclined axis. The tool axis of rotation forms, according to certain embodiments, together with the horizontal inclined axis in a horizontal projection, an acute angle which is greater than 0°.

The acute angle is in the angle range between 10 and 60° in various embodiments.

In contrast to known machines, which are designed for machining two workpieces using one tool, the grinding machine according to certain embodiments has a first horizontally extending linear axis (also called the horizontal inclined axis) which is set inclined in relation to the other (horizontal) axes of the machine. In addition, the two workpiece spindles are also accordingly arranged inclined. The first horizontally extending linear axis and the shared perpendicular of the two workpiece spindles are parallel to one another. It is an advantage of this unusual arrangement and axis configuration that in both machining positions, the cantilever arm length, which results by way of the infeed of the tool in parallel to the infeed axis in the direction of the workpiece, is equal. It is thus ensured that the manufacturing accuracy during the machining of the two workpieces is equal. In addition, this configuration may offer more space for the drive of the tool spindle.

According to certain embodiments, a first workpiece is machined on a first workpiece spindle and subsequently another workpiece is machined on a second workpiece spindle using a single (grinding) tool. After a first workpiece has been machined, a movable part of the machine together with the (grinding) tool mounted thereon executes a linear displacement, to move the (grinding) tool from a first machining position on the first workpiece into a second machining position on the second workpiece.

The machine may be designed in certain embodiments so that the machine can be automatically or semiautomatically charged with the workpieces. After the first workpiece has been machined, the tool carries out the machining of the second workpiece. In this time, the first workpiece can be removed and replaced by another workpiece (which is still to be machined). Similarly, the second workpiece can be removed and chucked again, while the first workpiece is machined.

As a result of this configuration, there may be sufficient space for a gripper, which is used for the automatic or semiautomatic handling of the workpieces. Optionally, the machine according to various embodiments is equipped with a handling device for introducing and/or removing workpieces

In such embodiments of the machine configuration, the (grinding) tool does not have to be re-chucked.

In further embodiments, the first workpiece spindle and the second workpiece spindle are designed to be stationary in relation to the grinding machine. In this case, the machine may include handling means for each of the workpiece spindles, to be able to execute the corresponding handling movements in conjunction with the introduction (charging) and/or removal of the workpieces.

The term stationary, as it is used here, permits only movements in or on the workpiece spindles, which are required in conjunction with the handling of the workpieces. Each workpiece spindle, in the scope of the handling, can chuck a workpiece (i.e., the workpiece spindle can open and close) and it can rotate the tool about the workpiece axis, for example. The workpiece spindles are fixed in relation to the machine bed in various embodiments, so that no displacement or shifting of the workpiece spindles in a horizontal plane is possible.

To relate the grinding tool to the respective workpiece during the grinding machining, infeed movements are required, and to move the grinding tool into an interaction with the respective workpiece and to create the desired (tooth) geometry, engagement and machining movements are necessary. These infeed, engagement, and machining movements are primarily executed by the tool and the axes which are associated with the tool, wherein the workpiece is rotationally driven about the workpiece axis of rotation.

With respect to quality and cost-effectiveness, the machine configuration may be suitable for the alternating continuous generating grinding of two workpieces. Continuous generating grinding is a generating method, in which a worm grinding wheel is used.

The machine configuration may offer the possibility of achieving good accuracy in the grinding machining, since the grinding machining is performed on both workpieces using the same grinding conditions.

Depending on the embodiment, the workpieces can be ground in synchronization or counter-rotation.

The grinding machines can be equipped in various embodiments with digital drive technology, both for the spindles and also the linear axes. Extremely high repetitive accuracies thus result.

A chronologically alternating workpiece change may be performed in various embodiments. The corresponding handling time is to be shorter in this case than the total time which is required for the movement of the tool from the first workpiece to the second workpiece and for machining the second workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details and advantages of the invention are described hereafter on the basis of exemplary embodiments and with reference to the drawing.

FIG. 1 shows a schematic perspective view of a conventional grinding machine, which is designed to perform grinding machining of a workpiece using a grinding tool;

FIG. 2A shows a schematic top view of a first grinding machine, which is designed to machine a first workpiece and subsequently a second workpiece using one grinding tool, wherein at the moment shown, the grinding tool is located in the region of the first workpiece (referred to as first machining position);

FIG. 2B shows a schematic top view of the first grinding machine, wherein at the moment shown, the grinding tool is located in the region of the second workpiece (referred to as second machining position);

FIG. 3 shows a schematic horizontal projection of the relevant axes of a grinding machine;

FIG. 4 shows a schematic front view of a second grinding machine, which is constructed similarly as the grinding machine according to FIGS. 2A and 2B;

FIG. 5 shows a schematic top view of a further grinding machine, wherein the grinding machine comprises a handling device.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Terms are used in conjunction with the present description which are also used in relevant publications and patents. However, it is to be noted that the use of these terms is only to serve for better comprehension. The concept of the invention and the scope of protection of the patent claims are not to be restricted in the interpretation by the specific selection of the terms. The invention may be readily transferred to other term systems and/or technical fields. The terms are to be applied accordingly in other technical fields.

A grinding machine 100 is equipped with a tool spindle 1 for receiving and rotationally driving a grinding tool 2 about a tool axis of rotation B (also referred to as tool axis in short). Furthermore, the grinding machine 100 comprises a first stationary workpiece spindle 3 for receiving a first workpiece W1 and a second stationary workpiece spindle 4 for receiving a second workpiece W2. The first axis of rotation C1, with which the first workpiece W1 is associated, and the second axis of rotation C2, with which the second workpiece W2 is associated, are perpendicular to the plane of the drawing of FIGS. 2A and 2B.

The structure in various embodiments can also be such that the workpiece axes are arranged horizontally instead of vertically (as shown in FIGS. 2A and 2B).

The first workpiece spindle 3 is designed for receiving a first workpiece W1 and the second workpiece spindle 4 is designed for receiving a second workpiece W2. As shown in FIGS. 2A and 2B, the first workpiece spindle 3 and the second workpiece spindle 4 are arranged on a shared longitudinal side of the grinding tool 2 received on the tool spindle 1. This longitudinal side is to the right of the cylindrical grinding tool 2 in the top view shown. On the opposite longitudinal side of the cylindrical grinding tool 2, carriages and other elements of the machine 100 are located, which mount and move the grinding tool 2.

The two workpiece spindles 3, 4 are arranged vertically. The axes of rotation C1 and C2 may extend in parallel to one another in various embodiments, as can be seen well in FIG. 4.

To be able to execute the infeed, engagement, and machining movements, which are required for generating grinding, for example, the tool spindle 1 is mounted so it is displaceable along a first linear guide 5. In FIGS. 2A and 2B, two guide structures extending in parallel are shown. In various embodiments, for example, rails or grooves can be used as linear guides in a known manner. The first linear guide 5 extends in parallel to a first horizontal axis Y. The horizontal inclined axis Y is arranged inclined to other horizontal axis, however (see also FIG. 3), or is arranged inclined in relation to axes which have been projected in a shared horizontal plane, respectively.

The machine 100 comprises a tool axis of rotation B, about which the (grinding) tool 2 is rotationally driven during the generating grinding. This tool axis B forms, together with the first horizontal axis Y in a horizontal projection, an acute angle W which is greater than 0°. A corresponding illustration of the relevant axes is shown in FIG. 3. The mentioned acute angle W is defined at the point of intersection of the two axes B and Y in a horizontal projection (the plane of the drawing here).

In various embodiments, the acute angle may be in the angle range between 10 and 60°. In the exemplary embodiment shown in FIG. 2A and FIG. 3, the acute angle W is approximately 15°.

The first workpiece spindle 3 and the second workpiece spindle 4 are both spaced apart at the same perpendicular horizontal distance al from the first horizontal axis Y (see also FIG. 3).

The shared perpendicular between the axes of rotation C1 and C2 extends in parallel to the first horizontal axis Y. In FIGS. 2A, 2B, and 3, the orientation of the shared perpendicular is shown by a dashed straight line, which connects the two parallel axes of rotation C1 and C2 to one another on the shortest path. The corresponding dashed straight line is identified with the reference sign YII, to indicate that it extends in parallel to Y. The shared perpendicular between the axes of rotation C1 and C2 defines the distance Ab, which is shown in FIG. 3.

The distance Ab of the two axes of rotation C1 and C2 (measured along the straight line YII, as shown in FIG. 3) may fulfill the specification in various embodiments that it is at least two times as great as the workpiece diameter of the workpieces W1, W2 viewed in the top view.

As can be seen on the basis of FIG. 1, especially for generating grinding, an entire array of further axes are required to be able to execute the necessary infeed, engagement, and machining movements.

The axis arrangement of an exemplary embodiment will now be explained on the basis of FIGS. 2A and 2B. A differentiation is made between a main axis and secondary axes. An axis which bears all other axes is referred to as the main axis. In the embodiments according to FIGS. 2A, 2B, and according to FIG. 3, the Y axis is used as the main axis in each case. This axis is also referred to as the horizontal inclined axis Y.

The machine 100 can be transferred from a first machining position into a second machining position by a linear movement along the horizontal inclined axis Y. The machine 100 is shown in the first machining position in FIG. 2A and in the second machining position in FIG. 2B. It can be seen in the direct comparison of the two FIGS. 2A and 2B that these two machining positions are identical, except for the different location in relation to the Y axis. That is to say, no other axial movements have to be executed. Therefore, the cantilever arm is the same in both machining positions. Therefore, inter alia, the torques, which act as a result of the heavy motor of the tool spindle 1 on the overall structure of the machine 100, are also equal.

The machine 100 comprises a machine bed 6, on which the first linear guide 5 and the two workpiece spindles 3, 4 are arranged so they are stationary. A fixed machine substructure or column is referred to as the machine bed 6 in various embodiments, as is well known.

The grinding machine 100 furthermore comprises a first linear carriage 7, which is mounted so it is movable along the first linear guide 5 in parallel to the horizontal inclined axis Y. In FIGS. 2A, 2B, the first linear guide 5 comprises two guide structures shown as examples, which are marked with the reference sign 5. Guide shoes can be arranged on the lower side of the first linear carriage 7, to enable sliding of the first linear carriage 7 along the guide structures. These guide structures extend in parallel to the above-mentioned horizontal inclined axis Y. This horizontal inclined axis Y is used as the main axis of the grinding machine 100.

The grinding machine 100 furthermore comprises a second (e.g., tower-like or column-like) linear carriage 8, which is mounted so it is horizontally movable on the first linear carriage 7. The second linear carriage 8 is movable in parallel to a second horizontal axis X. This second horizontal axis X is also referred to as the infeed axis and it extends, viewed in a horizontal projection, inclined in relation to the first horizontal axis Y. The second linear carriage 8 can be guided, for example, along guide structures, which are identified here with the reference sign 12. Guide shoes can be arranged on the lower side of the second linear carriage 8, to enable sliding of the second linear carriage 8 along the guide structures 12.

The grinding machine 100 furthermore comprises a third linear carriage 9, which is mounted so it is movable on the second linear carriage 8 in the exemplary embodiment shown. The third linear carriage 9 is movable in parallel to a first vertical axis Z, which stands vertically in space. The first vertical axis Z is also referred to as the stroke axis. The third linear carriage 9 is seated here in the exemplary embodiment shown on a front lateral surface of the second linear carriage 8. A view of this front lateral surface of the second linear carriage 8 is shown in the front view of FIG. 4.

The grinding machine 100 furthermore comprises a pivot table 10, which is mounted so it is pivotable about a third horizontal axis A. The third horizontal axis A is also referred to as the tool pivot axis. The pivot table 10 directly or indirectly carries the tool spindle 1. The third horizontal axis A is perpendicular, projected in a shared horizontal plane, to the tool axis of rotation B. In the position shown in FIGS. 2A, 2B, the end face 2.1 of the cylindrical tool 2 shown as an example points diagonally upward. The tool 2 shown as an example is a worm grinding wheel, which is not shown in greater detail in the figures, however.

The pivot table 10 may carry a fourth linear carriage 11 in various embodiments. The corresponding axis is referred to as the shift axis or as the Y1 shift axis. This Y1 shift axis is located on the pivot axis A and carries the tool spindle 1. In various embodiments, the Y axis is only used for the horizontal movement between the two working positions and only the Y1 shift axis (having lesser mass) has to be used for so-called shift movements. This fourth linear carriage 11 enables a linear displacement (shift movement) of the tool spindle 1 together with tool 2 in parallel to the tool axis B in a lateral plane. A plane which is perpendicular to the machine bed 6 or to the plane of the drawing is referred to as a lateral plane. This lateral plane is in the plane of the drawing in FIG. 4.

The previous description may also be transferred to the embodiment of FIG. 4. The embodiment of FIG. 4 differs from the embodiment of FIGS. 2A, 2B primarily by way of the structure of the secondary axes, which are carried by the pivot table 10.

The staggering of the various axes can also be implemented in another sequence. Thus, for example, the carriage 8 can be vertically movable in a lateral plane and can carry a carriage 9, which is movable on the carriage 8 in the horizontal direction.

The fourth linear carriage 11 can also have a configuration as shown in FIG. 4. For example, the fourth linear carriage 11 can have a basic shape (for example, rectangular) or can have a base body 11.1 which, as shown in FIG. 4, is located in a lateral plane of the machine 100. In FIG. 4, this lateral plane corresponds to the plane of the drawing. Guide structures can be arranged on the basic shape or the base body 11.1 on the front side, which faces toward the workpieces W1, W2. In the embodiment according to FIG. 4, two guide structures 14 extending in parallel to the B axis are used. The Y1 shift axis is therefore parallel to the B axis here.

Guide shoes can be arranged on the lower side of the tool spindle 1, to enable sliding of the tool spindle 1 along the guide structures 14.

The machine 100 is thus distinguished in that the tool spindle 1 is mounted via four linear guides 5, 12, 13, 14 and a pivot axis A so it is movable on the machine bed 6. The mentioned pivot axis A is perpendicular in this case to the first axis of rotation RA1 of the first workpiece spindle 3 and to the second axis of rotation RA2 of the second workpiece spindle 4.

It is an advantage of these unconventional arrangements and axis configurations of FIGS. 2A, 2B, and 4 that in both machining positions, the cantilever arm which results due to the infeed of the tool 2 in the direction of workpiece C1 or C2, is equal. It is thus ensured that the manufacturing accuracy during the machining of the two workpieces C1, C2 is equal. In addition, this special configuration offers more space for the drive of the tool spindle 1. It can be seen well above all in FIG. 4 that the tool spindle 1, together with the motor 1.1 arranged coaxially thereto, are protruding. If the second workpiece spindle 4 and the workpiece C2 were not arranged offset in relation to the first workpiece spindle 3, collisions of the tool spindle 1 or the motor 1.1 would thus occur with the second workpiece spindle 4 or with the workpiece C2.

In various embodiments, the machine 100 may comprise a handling device 20, which is designed for introducing and/or removing workpieces C1/C2. Since alternately first a workpiece C1 is machined on the workpiece spindle 3 and then subsequently a workpiece C2 is machined on the workpiece spindle 4 using the tool 2, there is sufficient time to remove a finished machined workpiece and to introduce a new workpiece (for example, a blank) and to chuck it on the corresponding spindle

Therefore, handling device 20 may be designed in various embodiments for alternately removing and introducing a workpiece on a first of the two workpiece spindles 3 and then for removing and introducing a workpiece on a second of the two workpiece spindles 4. For this purpose, this handling device 20 may be arranged equidistantly (at equal distance viewed in the horizontal direction) to the two workpiece spindles 3 and 4 in various embodiments.

A schematic example of a machine 100 is shown in FIG. 5, which is equipped with an exemplary handling device 20. This handling device 20 can have a gantry structure, for example, as shown in FIG. 5. This gantry structure may extend in parallel to the main axis Y, which extends at an incline, in various embodiments.

In various embodiments, the handling device 20 can comprise inner lock gates 21, 22, which can be displaced upward and downward in parallel to the x axis. In FIG. 5, these two lock gates 21, 22 have a trapezoid shape in the top view. The outlines thereof are shown by dashed lines. The lock gate 21 is associated with the workpiece C1 and the spindle 3. The lock gate 22 is associated with the workpiece C2 and the spindle 4. The lock gate 22 can be closed while the lock gate 21 is open during the machining of the workpiece C1 using the tool 2, and vice versa. Thus, for example, a gripper of the handling device 20 can be protected from flying chips and coolant.

In various embodiments, the handling device 20 can additionally or alternatively also comprise outer lock gates (not shown), which can be displaced upward and downward in parallel to the x axis. These outer lock gates may be moved up and down in differential mode to the inner lock gates 21, 22.

In various embodiments, the handling device 20 can comprise counter holders (not shown), which can be displaced upward and downward in parallel to the x axis, to be able to hold the respective workpieces C1, C2 from above in the axial direction.

In various embodiments, the handling device 20 can comprise a column or tower structure 23, which is arranged equidistantly to the two workpiece spindles 3, 4, and which carries a gripper 24 on a pivotable boom 25. A snapshot is shown in FIG. 5, in which the boom 25 together with gripper 24 is concerned with the introduction of a workpiece C2 into the workpiece spindle 4. After the machining of the workpiece C1 using the tool 2 is ended, the boom 25 together with gripper 24 is pivoted about a vertical axis VA of the handling device 20 into another position. The vertical axis VA may extend in parallel to the x axis. In FIG. 5, the boom is identified in this other position with the reference sign 25* and the boom 25 is indicated by dotted outlines.

As may be recognized by those of ordinary skill in the pertinent art based on the teachings herein, numerous changes and modifications may be made to the above-described and other embodiments of the present invention without departing from the spirit of the invention as defined in the claims. Accordingly, this detailed description of embodiments is to be taken in an illustrative, as opposed to a limiting sense. 

What is claimed is:
 1. An apparatus comprising: a grinding machine having a tool spindle adapted to receive and rotationally drive a grinding tool about a tool axis of rotation, a first workpiece spindle adapted to receive a first workpiece, and a second workpiece spindle adapted to receive a second workpiece, wherein the first workpiece spindle and the second workpiece spindle are arranged on one longitudinal side of the grinding tool received on the tool spindle, both workpiece spindles are arranged parallel to one another, the tool spindle is mounted so it is displaceable along a first linear guide, which extends in parallel to a horizontal inclined axis, and the first workpiece spindle and the second workpiece spindle are spaced apart at a same perpendicular horizontal distance from the horizontal inclined axis, wherein the tool axis of rotation forms, together with the horizontal inclined axis in a horizontal projection, an acute angle, which is greater than 0°.
 2. An apparatus according to claim 1, further comprising a machine bed, and a first linear guide, wherein the first linear guide and the two workpiece spindles are stationarily arranged.
 3. An apparatus according to claim 1, further comprising: a first linear carriage, which is mounted so it is movable horizontally along the first linear guide, and a second linear carriage, which is mounted so it is horizontally movable on the first linear carriage, wherein the second linear carriage is movable in parallel to a first horizontal axis, which, viewed in a horizontal projection, extends inclined to the horizontal inclined axis.
 4. An apparatus according to claim 3, further comprising: a third linear carriage, which is mounted so it is movable on the second linear carriage, wherein the third linear carriage is movable in parallel to a first vertical axis extending perpendicular to one or more of the first horizontal axis or the horizontal inclined axis.
 5. An apparatus according to claim 3, further comprising: a pivot table, which is mounted so it is pivotable about a horizontal pivot axis and which carries the tool spindle, wherein the horizontal pivot axis, projected in a horizontal plane containing the first horizontal axis, extends perpendicularly to the tool axis of rotation.
 6. An apparatus according to claim 5, wherein the pivot table carries a fourth linear carriage configured to enable a linear displacement of the tool spindle in parallel to the tool axis of rotation in a lateral plane that is perpendicular to a machine bed.
 7. An apparatus according to claim 1, further comprising a machine bed, wherein the tool spindle is mounted on the machine bed by four linear guides and pivotable about a pivot axis so that the tool spindle is movable on the machine bed, wherein the pivot axis extends perpendicularly to a first axis of rotation of the first workpiece spindle and perpendicularly to a second axis of rotation of the second workpiece spindle, and the first axis of rotation and the second axis of rotation are stationarily arranged on the machine bed.
 8. An apparatus according to claim 1, further comprising a handling device configured to one or more of introducing or removing workpieces in the grinding machine.
 9. An apparatus according to claim 8, wherein the handling device is arranged equidistantly to the first and second workpiece spindles, and the handling device is configured to alternately perform the handling of a first workpiece and then the handling of a second workpiece. 